LA GUAIRA : Emergency teams with rescue dogs were searching Sunday for any remaining survivors of powerful twin earthquakes that struck Venezuela, where the death toll has surpassed 1,450 and nearly 200 buildings have completely collapsed.

A man and his teen son were found alive under the rubble Sunday by French and American rescue teams in Caraballeda, a town about 40 kilometers north of Caracas, AFP journalists saw.

The rescue offered a glimmer of hope in an ongoing tragedy that has shaken a country already mired in an economic crisis, but tens of thousands of people were still reported missing and the critical 72-hour window for rescuing trapped victims following a natural disaster has now passed.

Millions more people were feared to lack sanitation and other basic needs after one of Latin America's most devastating earthquake disasters.

Rescue teams from the United States, Mexico and elsewhere scrambled to save people as desperate residents dug by hand for relatives trapped in the pancaked layers and rubble of collapsed apartments.

Some 774 buildings were badly damaged in back-to-back quakes of magnitude 7.2 and 7.5 that struck on Wednesday evening, including 189 buildings that have totally collapsed, National Assembly President Jorge Rodriguez said Sunday.

In one of the worst-hit areas, the coastal city of La Guaira, Hector Aguilera came to search for four family members buried in the rubble.

"We don't have the support to get our family out -- we can't do it alone. They are buried there: we know they are dead, but here we are," he said.

"We have no hope left; all I have are memories."

Experts say the first 72 hours after natural disasters define the narrow window for rescuing the living. After that the search usually becomes one of recovering bodies.

In the San Bernardino neighborhood of Caracas, volunteers clambered over a collapsed building, using drills to break up concrete and forming lines to remove rubble by hand.

In Chacao, another area of the capital, large electronic screens on a building usually used for advertising were showing the faces of missing people in a bid to help find them.

On Sunday, Rodriguez reported 1,450 dead -- a toll expected to rise -- with 3,150 people injured.

Even as rescue efforts continued apace, outbreaks of looting hit La Guaira, much of which now lies in rubble after Wednesday's disaster.

Pharmacies, supermarkets and other businesses were ransacked, said residents, some of whom complained of the slow and meager post-quake aid coming from authorities.

- 'Hold onto hope' -

Interim Venezuelan President Delcy Rodriguez on Sunday praised rescuers for still pulling survivors from the ruins.

"Today we have rescued people who are still alive, and therefore these efforts will not be suspended," she said.

"We always hold onto hope."

US helicopters ferried in aid, and 230 more US military personnel were arriving to help expand airport capacity and reopen a key seaport to boost relief efforts, the US Southern Command said Sunday.

The United States -- which captured Venezuela's former president Nicolas Maduro in a military raid on Caracas in January -- had already sent a 250-strong disaster response team.

But the prospect for rescuing more survivors has dwindled.

A Salvadoran rescue worker who declined to give his name put it this way: "At this point, they are probably dead bodies. Thanks to God maybe we can find people still alive."

Exasperation has boiled over in some locales where residents claim that authorities have not done enough to rescue earthquake victims.

"The country needs you. Put down your weapon," one man shouted to soldiers in the Tanaguarena area of hard-hit La Guaira state, urging them to pick up picks and shovels instead.

Facing public outrage at the response by local officials, Rodriguez thanked other countries for the outpouring of aid.

Twenty-four nations have sent 521 tons of supplies, 86 units with dogs trained to locate people trapped beneath the rubble and more than 2,700 search-and-rescue personnel, she said.

- Economic impact -

The UN migration agency said that based on population and damage data, up to 6.76 million people could be affected, and would require shelter, water, sanitation, healthcare and essential relief items.

Venezuela's worst earthquakes in more than a century have come after the oil-rich country endured more than a decade of economic collapse.

The crisis has hollowed out hospitals and public services, driving millions to leave the country.

The United Nations estimated $6.7 billion in physical damage -- equivalent to six percent of Venezuela's GDP.

On Sunday Venezuelan opposition figure Maria Corina Machado, currently in exile, announced she will return "very soon" to her homeland.

"The time has come," she told US broadcaster Fox News.

"We need to be together, to embrace, to grieve and mourn together, but also to give each other strength at this difficult time."